Most liquid crystal display devices are passive devices in which images are displayed by controlling an amount of light input from an outside light source. Thus, a separate light source (for example, backlight system) is generally employed for illuminating an LCD.
Generally, backlight systems can be classified into an edge lighting type or a bottom lighting type based upon the location of lamps within the devices. The edge lighting type backlight system has a lamp unit arranged at a side portion of a light guiding plate for guiding light. The edge lighting type backlight systems are commonly employed in small-sized LCD due to their lightweight, small size, and low electricity consumption. A bottom lighting type backlight system has a plurality of lamps arranged in regular positions to directly illuminate an entire surface of an LCD panel. The bottom lighting type backlight systems have higher efficiency of light usage than the edge lighting type backlight systems. The bottom lighting type backlight systems are especially used in large-sized LCD devices. However, an LCD device usually employs a significant amount of lamps to reach a high luminance. The significant amount of lamps results in a great deal of heat produced and cumulated inside the LCD device. Therefore, heat dissipation of the direct type backlight systems is usually a hard nut to crack.
Referring to FIG. 7, a typical bottom-lighting backlight system 10 is shown. The backlight system 10 includes a plurality of lamp tubes 110, a light diffusion plate 120, a reflective plate 130, a heat dissipation plate 140, and a frame 150. The frame 150 includes a rectangular base 151 and four connecting sidewalls 153 that extend out from a periphery of the base 153, the base 151 and the sidewalls 153 cooperatively defining a chamber 155. The reflective plate 130 is disposed in the chamber 155 of the frame 150 and separated away from the base 151. The heat dissipation plate 140 is fixed to a bottom surface of the reflective plate 130 facing the base 151. The lamp tubes 110 are aligned above the reflective plate 130 in the chamber 155. The light diffusion plate 120 is positioned on the sidewalls 153 and covers the chamber 155 for diffusing light emitting out of the lamp tubes 110, thus, producing a uniform surface light output.
Heat is efficiently dissipated out from fin structures (not labeled) of the heat dissipation plate 140 via the reflective plate 130, however the heat is still accumulated in the chamber 155. In addition, in order to enhance uniformity of light rays for the backlight system 10, there must be a big space defined between the diffusion plate 120 and the lamp tubes 110 for eliminating potential dark strips caused by the reduced intensity of light between adjacent lamp tubes 110. Therefore, the backlight system 10 suffers from increased thickness and decreased luminance due to the space exiting between the diffusion plate 120 and lamp tubes 110. Furthermore, the thickness of the backlight system 10 is also increased due to an employment of the reflective plate 130 and the heat dissipation plate 140.
What is needed, therefore, is a light source module and backlight system using the same that overcomes the above mentioned shortcomings.